Post on 30-Dec-2015
description
The stomach can be divided into three anatomic (A) and two functional regions (B)
Gastric reservoirTonic contractions Gastric reservoirTonic contractions
Gastric pumpPhasic contractionsGastric pumpPhasic contractions
BBFundusFundus
CorpusCorpusAntrumAntrum
PylorusPylorus
AA
Ehrlein Figure 1
The relaxation of the gastric reservoir is mainly regulated by reflexes. Three kinds of relaxation can be differentiated:
the receptive, adaptive and feedback-relaxation
Ehrlein Figure 2
Inhibitoryvagal fibre(NANC-inhibition)
Nutrients
CCKRelaxation of
gastric reservoir
ACH
Vaguscentre
1. Receptive relaxationMechanical
stimuli in the pharynx
3. Feedback relaxation
2. Adap tive relax ation
NutrientsTensionreceptors
Distension
NO + VIP et al.
The transport of digesta from the gastric reservoir into the antral pump is caused by two mechanisms: tonic contractions and peristaltic waves in the region of the gastric corpus
Ehrlein Figure 3
Tonic contraction
Peristaltic wave(Pump of the reservoir)Proximal
antrum
Backflow from antrum and flow from reservoir
Pylorus
Accumulationof chyme
The function of the gastric pump can be differentiated intothree phases: A: phase of propulsion, B: phase of emptying,C: phase of retropulsion and grinding
A Phase of propulsion Contraction of proximal antrum (PA)
B Phase of emptying Contraction of middle antrum (MA)
Propulsion of chyme into relaxingterminal antrum
+ duodenal contraction
Transpyloric and retrograde flow+ duodenal relaxation
C Phase of retropulsion Contraction of terminal antrum (TA)
Jet-like back-flow with grinding+ duodenal contraction
Phases
A B C
10 sec
Proximalantrum
Middleantrum
Terminal antrum
Pylorus
Duodenum
Pylorus
PA
MA
TA
closed
open
Ehrlein Figure 4
Liquids and small particles leave the stomach more rapidly than large particles.
This discrimination is called „sieving function“
Retropulsion of largeparticles and clearingof the terminal antrum
Phase of propulsion Phase of retropulsionPhase of emptying
Bulge
Rapid flow of liquids withsuspended small particlesand delayed flow of largeparticles towards pylorus
Emptying of liquids withsmall particles whereaslarge particles are retainedin the buldge of the terminalantrum
Antrum
Ehrlein Figure 5
Grinding of solid particles is caused by a forceful jet-like retropulsion through the small orifice of the
terminal antral contraction
Onset of terminal antral
contraction
Pylorus closing
Late phase of terminal antral
contraction
Pylorus closed
Ehrlein Figure 6
Antro-duodenal co-ordination: Contractions of the proximal duodenum cease during the phases of gastric emptying..
Ehrlein
Antralwaves
Middle antrum
Terminal antrum
Pylorus
Proximalduodenum
Lacking duodenal contractions
0 5 10 15 20 25 30 35 sec
1
Phases of gastric emptying
3.59.9 3.5 9.96.6open
closed
2 1 1 13 3 32 2 4
Figure 7
Because of different frequencies between antral and duodenal contractions,the duodenum can contract three to four times during an antral wave
sec
Several factors of gastric and duodenal motility co-operate and modulate gastric emptying:
Ehrlein
A. Rapid emptying is caused by tonic contractions of the reservoir (1a), deep peristaltic waves along the gastric body (1b), deep constrictions of the antral waves (2), a wide opening of the pylorus (3), a duodenal receptive relaxation (4) and peristaltic duodenal contractions (5). B. Delayed emptying due to feedback inhibition is caused by a prolonged relaxation of the reservoir (6a), shallow peristaltic waves along the gastric body ( 6b), shallow antral waves (7), a small pyloric opening (8), a lacking duodenal relaxation (9) and segmenting duodenal contractions (10).
Figure 8
510
A. Rapid emptying
Pylorus1a
1b2
34
7
89
B. Delayed emptying
6a
6b
Balance between gastric reservoir and antral pump
Figure 9Ehrlein
Gastro-gastric reflexes
Excitatory reflex
Inhibitoryreflex
Enhanced and prolonged relaxation of reservoir
Distension
Antral pump switched on
and intensified
Disten-sion
Pyloric activity is modulated by antral inhibitoryand duodenal excitatory reflexes
Figure 10Ehrlein
Descendinginhibitory reflex
causing pyloric relaxation
Contraction of middle antrum
Ascendingexcitatory reflex
causing pyloric contractions
and increasing pyloric tone
Duodenal stimuli
An additional function of the pyloric sphincter is to prevent duodeno-gastric reflux
Figure 11
Pyloric closure
Inhibition
Stimulation
0.5 ml oleic acid + bile into duodenum
Antrum
Pylorus
Duod. bulb
Duodenum
closed
open
Ehrlein
Duodenal stimuli like oleic acid inhibit antral contractions, evoke duodenal contractions, increase pyloric tone and elicit frequent pyloric contractions
Solids and liquids of the gastric chyme are emptied with different velocities.
Ehrlein
Lag phase
Time (min)
Viscouscontent
Liquid content
Solids100
80
60
40
20
00 20 40 60 80 100 120
Gas
tric
vo
lum
e ( %
)
Figure 12
Emptying of liquids is exponential, emptying of large solid particles only begins after sufficient grinding (lag phase). Afterwards the viscous chymeis mainly emptied in a linear fashion
Nutrients in the gut activate a feedback control and modulate gastric and duodenal motility
Ehrlein Figure 13
Gastrointestinal motor patterns after a non-caloric and a nutrient meal
Antrum
Pylorus
closed
open
Duodenalbulb
MiddleDuodenum
Reduced force ofantral contractions
Reduced pyloric opening
Reduced peristaltic waves
Enhancedsegmenting activity
Non-caloric meal Nutrient meal
Feedback control causes
The feedback regulation of gastric emptying is performed by entero-gastric reflexes and release of intestinal hormones
Ehrlein Figure 14Ehrlein Figure 14
It causes enhanced relaxation of the gastric reservoir, inhibition of the antral pump, and reduced opening of the pyloric sphincter.
Vagalcenter
Inhibitoryvagal fibers
NO, VIP et al.
Senso
ric
affe
rent
fiber
s
CCK
ACHEnhancedrelaxation
andstorage
Stimulating cholinergicvagal fibers
Nutrients Long chain fatty acids Amino acids Dipeptids GlucoseOsmolalityHydrochloric acid
Reduced openingof pyloric sphincter
Reduced contraction
Backflow
+
+_
ACH
Contractile patterns of the small intestine
Ehrlein
Peristaltic Stationary Clusterswaves contractions of contractions
1 minute 1 minute 1 minute
oral
aboral
Figure 15
The most frequent patterns are peristaltic waves (dashed lines), stationary contractions (arrows), and clusters of contractions, which occur either stationary at an intestinal segment or slowly migrate aborally
Phase III of the interdigestive motility designated as ”migrating motor complex” (MMC)
oral
aboral Aboral migration of phase III
Velocity of the peristaltic waves
1 minuteJejunal phase III (MMC)
Ehrlein Figure 16
Rectangles: strain gauge transducers, Data of dog.
Pathological contractile patterns of the proximal intestine
Antiperistaltic waves
1 minute
Jeju
num
oral
aboral
Aboral giant contractions
1 minute
0,2 Newton
Duo
denu
m
oral
aboral
Ehrlein Figure 17
Alternating peristaltic (blue arrows) and antiperistaltic waves (red arrows). Giant contractions sometimes originate as a cluster.
Ehrlein Figure 18
Different kinds of contractile patterns are caused by different kinds of excitation
Excitation Excitation
PP 1
2
3
1
2
3
PP
Stationary Singlesegmenting contractions peristaltic waves
1, 2, 3 successive pacesetter potentials (PP)
Stationary segmenting contractions are produced by brief excitation of ashort intestinal segment
Single peristaltic waves are produced by short excitations of a long intestinal segment
Time course
Clustered contractions are produced by a long lasting excitation of a short intestinal segment. The cluster is stationary when the excitation remains at the same segment. When the excitation slowly moves aborally the cluster of contractions migrates along the intestine.
Stationary cluster Migrating cluster
Time course
Stationary excitation Aboral migrating excitation
1
2
3
1
2
3
Ehrlein Figure 19
Origin of clustered contractions
1, 2, 3 successive pacesetter potentials (PP)
Luminal stimuli elicit vago-vagal reflexes which activate integrating and program circuits of the enteric nervous system. These activate specific motorneurones responsible for specific contractile patterns.
Ehrlein Figure 20
Central and peripheral control of contractile patterns
Intestinalwall
Vagalcentre
Intestinallumenl
Peptide (CCK) ReceptorsGlucose - OsmolalityLong chain fatty acidsAmino acids
Sensory neurons
Vago-vagal reflexes
InterneuronsIntegrating circuits
Program circuits
Enteric nervous system
Motorneurons Contractilepatterns
Postprandial contractile patterns of the small intestine
0,2 Newton
oral
aboral
Ehrlein Figure 21
They are composed of stationary segmenting contractions (green arrows), stationary and migrating clusters of contractions (red horizontal lines)
and single short peristaltic waves (dotted lines).
The phase III of the migrating motor complex originates simultaneously at the stomach and duodenum and migrates within 90 to 120 minutes along the small intestine (dog)
Interdigestive CyclesPhases
Sporadicperistaltic waves
Segmenting contractionsand single
peristaltic waves
Motorquiescence of stomach
and duodenum
Contractionof reservoir
Pylorus
Aboral migration
Accumulation of residues
of chyme
Phase IIPhase I
Stomach
Duodenum
Jejunum
Ileum
Phase III
Phase III
III I II III
Phase III
Phase II
Phase I
Forcefulperistaltic
waves
Motorquiescence
Ehrlein Figure 22
The interdigestive motility consists of three phases
The antral waves are associated with a wide opening of the pylorus and inhibition of duodenal contractions followed by duodenal peristaltic waves occurring at maximal frequency.
Ehrlein Figure 23
Middle Antrum
Pyloric diameter
Duodenal bulb
Duodenum
Gastric phases III
1 min
PAP P
0 mm
6 mm
Stomach is cleaned of residues of chyme and secretions.
Gastric phase III consisting of 1 - 3 forceful contractions of the gastric reservoir and lumen occluding peristaltic
waves occurring at intervals of 2-3 min
Phase III (MMC) of the small intestine
Ehrlein
Intestinal phase III
oral
Successsiveperistaltic waves
Chyme
Slow aboralmigration of phase III
aboral
Time (about 20 sec)
Time (about 20 sec)
Figure 24
The peristaltic waves clean the intestinal segment from chyme which accumulates aborally. Because the successive waves start and end further aborally the phase III slowly migrates distally
Postprandial motility is characterised by a lower amplitude of the antral waves occurring at maximal frequency, rhythmic pyloric opening and closure and co-ordinated duodenal contractions occurring in sequencewith the antral waves
Ehrlein
Antrum
Pylorus
Duodenum
5 min
MealPhase III
closed
open
Fed motor pattern
Figure 25
Ingestion of a meal suppresses the interdigestive motility and induces a fed motor pattern
C: A special feature of the large intestine are multiple segmenting contractions of long duration migrating aborally. They divide digesta into boli pushing them slowly aborally. The motility tracings show a rise of the baseline superimposed by phasic contractions
C: A special feature of the large intestine are multiple segmenting contractions of long duration migrating aborally. They divide digesta into boli pushing them slowly aborally. The motility tracings show a rise of the baseline superimposed by phasic contractions
Ehrlein Figure 26
Contractile patterns of the large intestine
AA
BB
CC
Colonic segmenting contractions migrating aborally
aboral migration
small aboral flow
backflow low propulsion
Shallow peristaltic waves of caecum and colon
Shallow peristaltic waves at haustrated colon
slow aboral propulsion
Motility of the large intestine in pig
A: Haustral movements of the caecum result in clustered contractions. B: The ileum is emptied by giant contractions. They occur either isolated or in co-ordination with peristaltic waves of the caecum and colon. Additional colonic waves originate at the beginning of the colonic coil.
Caecum
Ehrlein
J1J2
C1 C2 C3
Co1
Co2
Co3
Ileum
Colon
Distal colon
Caecum
C1
C2
C3
1 min
Ileum - Caecum - Colon
1 min
Co3
Co1
Co2
C1
J2
J1Giant contractions
Colonic wave
Figure 27
AA BB
SC1
SC2
SC3
Spiral colon
Peristaltic wave
Caecal motility is characterised by peristaltic andantiperistaltic waves. In the colon peristaltic wavesand giant contractions are the dominant feature. Inthe spiral colon prolonged segmenting contractionsdivide digesta into boli and push them distally.
CaecumColon
Co1
Co2 Co3
Co4
C2 C3 C4
Ileum
SC1
SC2SC3
C1
Co2
Spiral colon
Caecum Colon
C4
C3
C2
C1
Co1
Co2
1 min1 min
Co3
C1
Co1
Co2
Co4
Giantcontraction
Ehrlein Figure 28
Motility of caecum and colon in sheep.
J1
C1
C2
C3
C4
C5
1 min
Colon
Co1
Co2
Co3
Giant contractions
1 min
Caecum
Caecal motility is characterised by peristaltic and antiperistaltic waves. Migrating segmenting contractions are the dominant feature of the single haustrated colon.
Co3J1 Co2
Co1
C1
C2
C3 C4 C5
Colon
Caecum
Ileum
Ehrlein Figure 29
Motor patterns of the large intestine in rabbits
A: Slow paper speed. The CMC’s occur at all parts of the colon at intervals of 20-30 min. B: High paper speed. The CMC’s consist of a rise of the baseline super-imposed of phasic contractions. The onset of the CMC‘s obviously differs along the colon (indicated by lines).
A: Slow paper speed. The CMC’s occur at all parts of the colon at intervals of 20-30 min. B: High paper speed. The CMC’s consist of a rise of the baseline super-imposed of phasic contractions. The onset of the CMC‘s obviously differs along the colon (indicated by lines).
Ehrlein
AA BBColonic motor complex (CMC)
aboral
oral
Phasiccontractions
15 min 5 min
Figure 30
Colonic motor complexes (CMC’s) of the canine colon
(1) Normal segmenting contractions of the proximal jejunum (2) Start of a retrograde giant contraction in proximal jejunum; (3) Retropelled digesta reach the duodenum and (4) are forced across thewidely opened pylorus into the antrum; (5) The giant contraction proceeds to the antrum, the chyme accumulates in the gastric reservoir.
1 2 34 5
1 2 3 4 5
Antrum
Pylorus (P)
Bulbus
Prox. duod.
Distal duod.
closed
open
1 min
Retrograde giant contraction Vomiting
Duodenum
P
P
Stomach
P
Jejunum
Ehrlein Figure 31
Retrograde giant contraction followed by vomiting